Facebook pays female staff in Britain just 0.8 percent less on average than male employees, but womens' bonuses are almost 40 percent lower.
The mean average disparity in pay is worse at Google's U.K. arm, where women are paid on average 17 percent less than men. Google's average bonus for female staff is 43 percent lower than male staff.
All companies with more than 250 U.K. employees have to disclose their gender pay gaps by April 4.
Amazon also released gender pay gap figures Thursday for its various U.K. subsidiaries. It pays women an average of six percent less than men across its local workforce.
The company also broke out its U.K. subsidiaries, such as Amazon Video, which pays women on average 40 percent less than men, but its Amazon U.K. Services. business pays women just 2 percent less, better than that of the parent company's combined workforce average.
Among Facebook's top quartile—or highest paid staff—about 30 percent are women. This decreases to just 19 percent in the second quartile, according to data published by the company. For Amazon Video, the figures are about 39 percent and 50 percent respectively, while Amazon U.K. Services hovers about the 30 percent mark for both of the top two quartiles.
The largest difference for the top percentile in Amazon's report was within its London Development Center unit, where just 8.2 percent of the highest earners are women. Within this division, more women receive bonuses compared to men—98 percent versus 95 percent—but female employees received a mean bonus pay 12 percent lower than male colleagues.
In a statement Thursday, the e-commerce giant said that using the median average rather than the mean, its own gender pay gap analysis for the collective Amazon U.K. workforce showed it paid women 0.7 percent more than men, however.
"We have programs that we're continually working to further improve, to actively recruit and help advance more women into senior and technology-focused roles as we grow our business here in the U.K.," an Amazon spokesman said in the statement.
Staff at the U.S. tech giants are among some of the best paid in the U.K. Around 1,000 people work for Facebook U.K., sharing pay of 207 million pounds ($290 million) over 2016, according to the latest available accounts.
Fiona Mullan, head of European human resources at Facebook, said the pay gap was due to the company's engineering workforce, which represents over half of Facebook's employees in the U.K., and that more men are in senior leadership positions.
"Technical roles also tend to drive higher market rates of pay, both in terms of salary and total compensation, due to the demand for specialized skills," Mullan said.
As of Friday, 6,356 of an expected 9,000 companies had submitted data to the government website. Among other companies known for out-sized paychecks, Goldman Sachs Group reported a U.K. pay gap of 56 percent, while Citigroup pays U.K. females 44 percent less than male employees on average.
-- Bloomberg News